Field of the Invention
The present invention relates to an optical phase difference component (wave plate or retardation plate), a composite optical component (composite optical member) incorporating the optical phase difference component, and a method for manufacturing the optical phase difference component.
Description of the Related Art
Optical phase difference plates have so many uses, and are used for various uses such as reflective liquid crystal display devices, semi-transmissive liquid crystal display devices, pickups for optical disks, and PS conversion elements.
Examples of the optical phase difference plates include those formed by doubly refracting crystal or birefringent crystal that originally exists in the nature, such as calcite, mica, and crystal, those formed by a birefringent polymer, and those formed by artificially providing a periodic structure shorter than a wavelength to be used.
The optical phase difference plate formed by artificially providing the periodic structure is exemplified by an optical phase difference plate provided with a concave-convex structure (concave and convex structure) on a transparent substrate. The concave-convex structure used for the optical phase difference plate has a period (pitch) shorter than a wavelength to be used, and has a pattern such as a stripe pattern as depicted in FIG. 6. Such a concave-convex structure has refractive index anisotropy. When light enters an optical phase difference plate 400 depicted in FIG. 6 vertically to a substrate 420 of the optical phase difference plate 400, a polarization light component parallel to a periodic direction of the concave-convex structure and a polarization light component vertical to the periodic direction of the concave-convex structure travel in the concave-convex structure at different speeds. This generates a phase difference (retardation) between the two polarization light components. Such a phase difference may be controlled, for example, by a height (depth) of the concave-convex structure and the difference in refractive index between a material of convex portions and a material (air) of gaps between convex portions. The optical phase difference plate to be used in the above-listed devices such as the display devices is required to generate a phase difference of λ/4 or λ/2 (λ represents a wavelength to be used) to a wavelength to be used λ. In order to form the optical phase difference plate that can generate such a sufficient phase difference, there is a need to considerably increase the height (depth) of the concave-convex structure and the difference in refractive index between the material of convex portions and the material (air) of gaps between convex portions. Japanese Examined Patent Publication No. H07-99402 and Japanese Patent Application Laid-open No. 2005-10377 each disclose an optical phase difference plate in which a surface of a concave-convex structure is coated with a high refractive index material.